Commit 61b87cae authored Dec 07, 2015 by Stephane Eranian Committed by Ingo Molnar Jan 06, 2016

perf/x86: Fix filter_events() bug with event mappings



This patch fixes a bug in the filter_events() function.

The patch fixes the bug whereby if some mappings did not
exist, e.g., STALLED_CYCLES_FRONTEND, then any event after it
in the attrs array would disappear from the published list of
events in /sys/devices/cpu/events. This could be verified
easily on any system post SNB (which do not publish
STALLED_CYCLES_FRONTEND):

	$ ./perf stat -e cycles,ref-cycles true
	Performance counter stats for 'true':
              1,217,348      cycles
	<not supported>      ref-cycles

The problem is that in filter_events() there is an assumption
that the argument (attrs) is organized in increasing continuous
event indexes related to the event_map(). But if we remove the
non-supported events by shifing the position in the array, then
the lookup x86_pmu.event_map() needs to compensate for it, otherwise
we are looking up the wrong index. This patch corrects this problem
by compensating for the deleted events and with that ref-cycles
reappears (here shown on Haswell):

	$ perf stat -e ref-cycles,cycles true
	Performance counter stats for 'true':
         4,525,910      ref-cycles
         1,064,920      cycles
       0.002943888 seconds time elapsed

Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: jolsa@kernel.org
Cc: kan.liang@intel.com
Fixes: 8300daa2 ("perf/x86: Filter out undefined events from sysfs events attribute")
Link: http://lkml.kernel.org/r/1449516805-6637-1-git-send-email-eranian@google.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 72469764

arch/x86/kernel/cpu/perf_event.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -1534,6 +1534,7 @@ static void __init filter_events(struct attribute **attrs)
		{
		struct device_attribute *d;
		struct perf_pmu_events_attr *pmu_attr;
		int offset = 0;
		int i, j;

		for (i = 0; attrs[i]; i++) {
		@@ -1542,7 +1543,7 @@ static void __init filter_events(struct attribute **attrs)
		/* str trumps id */
		if (pmu_attr->event_str)
		continue;
		if (x86_pmu.event_map(i))
		if (x86_pmu.event_map(i + offset))
		continue;

		for (j = i; attrs[j]; j++)
		@@ -1550,6 +1551,14 @@ static void __init filter_events(struct attribute **attrs)

		/* Check the shifted attr. */
		i--;

		/*
		* event_map() is index based, the attrs array is organized
		* by increasing event index. If we shift the events, then
		* we need to compensate for the event_map(), otherwise
		* we are looking up the wrong event in the map
		*/
		offset++;
		}
		}